Method for producing tungsten

ABSTRACT

Provided is a method for efficiently producing tungsten from a raw material mixture comprising at least one valuable containing tungsten. The present invention relates to a method for producing tungsten, comprising the steps of subjecting a raw material mixture comprising at least one valuable containing tungsten to electrolysis using an organic electrolytic solution to dissolve tungsten in the electrolytic solution; and calcining the electrolytic solution containing dissolved tungsten at a temperature of less than 800° C. to obtain tungsten.

TECHNICAL FIELD

The present invention relates to a method for producing tungsten.

BACKGROUND ART

A recovery method of metals usually involves a process of crushing scrapcontaining the metals and dissolving them in an alkaline solution.However, in the recovery of tungsten, applying such a conventionalprocess is very difficult because tungsten is a very hard and highlychemical resistant metal. Therefore, it is a common method in the artthat tungsten is oxidized by a strong treatment with alkali molten saltsor the like to dissolve and recover tungsten (Patent Document 1, PatentDocument 2 and the like).

In the common method, a tungsten-used target and an end material areoriginally high purity, so that the use of the molten salt treatment orpulverization which is the general treatment as described above willlead to significant reduction of purity. Therefore, in order to providetungsten with high purity, multistage purification, ion exchangetreatment and the like will be required, thereby leading to complicatedtreating steps.

Electrolysis is known as the method for dissolving tungsten. To recovertungsten with high purity, ammonium nitrate that is an inorganicsolution would be considered to be used for the electrolytic solution.However, it is necessary to separately add ammonia to adjust a pH of theelectrolytic solution in order to carry out alkaline electrolysis.

However, ammonium nitrate itself increases a risk of explosion at highconcentration. It is thus necessary to control the concentration ofammonium nitrate during electrolysis. Furthermore, since ammonia alsohas a concentration change due to volatilization in an electrolysistemperature range, concentration control and the like are necessary, sothat running costs are required for recovery equipment, controlequipment and the like. In addition, an impurity-free treating method isrequired for the recovery of tungsten from materials having originallyhigh purity, such as used targets and end materials.

To solve the above problems, the present inventors previously found thattungsten with high purity could be recovered with a low cost by carryingout electrolysis using an alcohol amine-containing electrolytic solution(Patent Document 3).

CITATION LIST Patent Literature

Patent Document 1: Japanese Patent Application Laid-Open Publication No.2011-047013 A1

Patent Document 2: Japanese Patent Application Laid-Open Publication No.2013-194269 A1

Patent Document 3: Japanese Patent No. 5329615 B1

SUMMARY OF THE INVENTION Technical Problem

Patent Document 3 produces WO₃ or W having high purity by converting atungsten component into a hydroxide by electrolysis of a raw materialmixture to dissolve the hydroxide in an electrolytic solution,concentrating the hydroxide to form a tungstate salt compound andoptionally heating and reducing the compound. However, there stillremains a need for a method of efficiently producing tungsten from theraw material mixture comprising at least one valuable containingtungsten.

Therefore, an object of the present invention is to provide a method forefficiently producing tungsten from a raw material mixture comprising atleast one valuable containing tungsten.

Solution to Problem

As a result of intensive studies to solve the above problems, thepresent inventors have found that tungsten can be efficiently producedby subjecting a raw material mixture comprising at least one valuablecontaining tungsten to electrolysis using an organic electrolyticsolution to dissolve tungsten in the electrolytic solution and thencalcining it at a controlled temperature.

In one aspect, the present invention completed on the basis of the abovefindings provides a method for producing tungsten, comprising the stepsof subjecting a raw material mixture comprising at least one valuablecontaining tungsten to electrolysis using an organic electrolyticsolution to dissolve tungsten in the electrolytic solution; andcalcining the electrolytic solution containing dissolved tungsten at atemperature of less than 800° C. to obtain tungsten.

In an embodiment of the method for producing tungsten according to thepresent invention, the organic electrolytic solution may be an organicalkaline electrolytic solution.

In another embodiment of the method for producing tungsten according tothe present invention, the organic alkaline electrolytic solution maycontain at least one alcohol amine.

In a further embodiment of the method for producing tungsten accordingto the present invention, the at least one alcohol amine may bemonoethanolamine and/or triethanolamine.

In yet another embodiment of the method for producing tungsten accordingto the present invention, the raw material mixture may contain from 1 to30% by mass of at least one valuable other than tungsten.

In yet another embodiment of the method for producing tungsten accordingto the present invention, the raw material mixture may contain from 1 to10% by mass of at least one valuable other than tungsten.

In yet another embodiment of the method for producing tungsten accordingto the present invention, the raw material mixture may contain from 3 to10% by mass of at least one valuable other than tungsten.

In yet another embodiment of the method for producing tungsten accordingto the present invention, the electrolysis may be carried out byadjusting a temperature of the electrolytic solution to 20 to 80° C.

In yet another embodiment of the method for producing tungsten accordingto the present invention, the electrolytic solution may have a pH of 7or more.

In a further embodiment of the method for producing tungsten accordingto the present invention, tungsten carbide may be obtainedsimultaneously with the tungsten in the step of calcining theelectrolytic solution containing dissolved tungsten at the temperatureof less than 800° C. to obtain tungsten.

In yet another embodiment of the method for producing tungsten accordingto the present invention, after the step of dissolving tungsten in theelectrolytic solution, the electrolytic solution may be subjected topreliminary heating to reduce water content, and then carrying out thecalcining step to obtain tungsten.

In a further embodiment of the method for producing tungsten accordingto the present invention, an anode used for the electrolysis may be atitanium basket provided with the raw material mixture containing the atleast one valuable containing tungsten.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a methodfor efficiently producing tungsten from a raw material mixturecomprising at least one valuable containing tungsten.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an example of an electrolytic bathaccording to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between constant voltage andcurrent efficiency in electrolysis.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the method for producing tungsten accordingto the present invention will be described in detail.

First, a raw material mixture to be treated is prepared, which containsat least one valuable containing tungsten. Examples of the raw materialmixture containing the at least one valuable containing tungsten includeso-called tungsten recycled materials obtained by pulverizing tungstenscrap and the like. For example, the raw material mixture containing theat least one valuable containing tungsten to be treated according to thepresent invention may contain from 0 to 15% by mass of Co, from 0 to 5%by mass of Ni, from 0 to 5% by mass of Fe, from 0 to 5% by mass of Ti,and form 0 to 15% by mass of Ta, and have the tungsten content of from 3to 95% by mass. Further, the raw material mixture containing the atleast one valuable containing tungsten to be treated according to thepresent invention may contain from 1 to 30% by mass of at least onevaluable other than tungsten, or from 1 to 10% by mass of at least onevaluable other than tungsten, or from 3 to 10% by mass of at least onevaluable other than tungsten.

Then, an electrolytic bath provided with an anode, a cathode and anelectrolytic solution is prepared, and the bath is used to carry outelectrolysis of the raw material mixture containing the at least onevaluable containing tungsten.

The electrolytic bath is not particularly limited, but may be, forexample, the configuration as shown in FIG. 1. In FIG. 1, a titaniumbasket is used as the anode, and the raw material mixture containing theat least one valuable containing tungsten is provided in the titaniumbasket. The titanium basket is preferable in that it is stable underhigh voltage, high current and high temperature electrolytic processingconditions of the present invention.

The electrolytic solution employs an organic electrolytic solution. Theorganic electrolytic solution may be preferably an alkaline electrolyticsolution, and more preferably may contain at least one alcohol amine.

Further, the electrolytic solution that can be used includes anelectrolytic solution containing an alcohol amine having 1 or more andless than 6 carbon atoms. The alcohol amine having 1 or more and lessthan 6 carbon atoms may be one or more selected from the groupconsisting of methanolamine, ethanolamine, propanolamine, butanolamine,pentanolamine, dimethanolamine, diethanolamine, trimethanolamine,methylmethanolamine, methylethanolamine, methylpropanolamine,methylbutanolamine, ethylmethanolamine, ethylethanolamine,ethylpropanolamine, dimethylmethanolamine, dimethylethanolamine,dimethylpropanolamine, methyldimethanolamine, methyldiethanolamine anddiethylmethanolamine.

In particular, the use of the electrolytic solution containing thealcohol amine having 1 or more and less than 6 carbon atoms can allowtungsten to be produced with good efficiency and yield when carrying outa subsequent calcining step of a tungstate solution.

Further, the electrolytic solution that can be used for the presentinvention includes an electrolytic solution containing an alcohol aminehaving 6 carbon atoms, which is one or more selected from the groupconsisting of hexanolamine, dipropanolamine, triethanolamine,methylpropanolamine, ethylbutanolamine, propylpropanolamine,butylethanolamine, pentylmethanolamine, dimethylbutanolamine,diethylethanolamine, methylethylpropanolamine, methylpropylethanolamineand ethylpropylmethanolamine. Thus, the use of the electrolytic solutioncontaining the alcohol amine having 6 carbon atoms can allow tungsten tobe produced with good efficiency and yield when carrying out thesubsequent calcining step of the tungstate solution.

Further, when the alcohol amine is used in the electrolytic solution asdescribed above, the treatment reaction system of electrolysis does notcontain impurities such as Na, K, Fe and S, so that tungsten having highpurity can be recovered. Further, tungsten having purity of 4N or morecan be obtained from the recycled materials and the like. In addition,the electrolytic solution has high voltage endurance and is stable, andalso has low pH dependency, so that easy controlling of electrolysis canbe achieved, and the electrolytic solution does not need supplement dueto volatilization that will be required when the electrolytic solutionis ammonia, so that a low cost processing can be achieved. Although aclear reason why the alcohol amine electrolytic solution has highvoltage endurance and is stable is not known, the reason would bepossibly because the electrolytic solution is stabilized by coordinatingthe dissolved tungsten with the alcohol amine.

The concentration of the alcohol amine in the electrolytic solution maybe preferably from 1 to 80% by mass. If the concentration of the alcoholamine in the electrolytic solution is less than 1% by mass, conductivitywill excessively decreased and electrolysis will become unstable, sothat complex formation may be difficult. If the concentration of thealcohol amine in the electrolytic solution is more than 80% by mass,solubility in water will be exceeded depending on the type of theelectrolytic solution and the concentration will be unnecessarilyincreased, which will be disadvantageous in terms of costs. Theconcentration of the alcohol amine in the electrolytic solution may bemore preferably from 2 to 50% by mass, and still more preferably from 5to 40% by mass, and still more preferably from 5 to 20% by mass.

The temperature of the electrolytic solution during electrolysis may beadjusted to 20 to 80° C. to carry out the electrolysis. The temperatureof the electrolytic solution of 20 to 80° C. may stabilize the alcoholamine and satisfactorily suppress volatilization of the alcohol amine.Therefore, the points where the electrolytic solution does notvolatilize and is stable and has few impurities in the electrolysisreaction are very advantageous for the processes of recovering tungstenhaving high purity and separating and recovering other valuables, interms of a total cost. The temperature of the electrolytic solution maybe more preferably set to an elevated temperature of 60° C. or higher interms of the electrolysis rate. For example, ammonia aggressivelyvolatilizes at 50° C. or higher and requires a large amount ofsupplement, but the alcohol amine based electrolytic solution has ahigher boiling point and is hard to volatilize, so that the alcoholamine based electrolytic solution can be used at 60° C. or higherwithout any problem.

The pH of the electrolytic solution may be preferably 7 or more. If thepH is less than 7, a produced tungstate ion will become difficult to bedissolved, and will be precipitated as WO₃ or H₂ WO₄, and as a result,electrolytic dissolution may be inhibited. More preferably, theelectrolytic solution may be adjusted such that the electrolyticsolution is weakly alkaline with a pH of 10 or more, for example.

The alcohol amines used in the electrolytic solution have high voltageendurance and high current density resistance. For high productivity,higher set voltage and higher set current density in electrolysis ispreferred, but practically, the set voltage may be 20 V or less and theset current density may be 500 A/dm² in view of limitations offacilities and damages to the cathode side. As a reference, FIG. 2 showsthe relationship between constant voltage and current efficiency in theelectrolysis.

Thus, by conducting electrolysis of the raw material mixture containingthe at least one valuable containing tungsten using the electrolytesolution containing the alcohol amine, tungsten can be dissolved in theelectrolytic solution while at the same time electrodepositing a part ofthe valuable(s) onto the cathode used for the electrolysis. Further, theat least one valuable other the valuable(s) electrodeposited onto thecathode by the electrolysis can be a residue in the electrolyticsolution. Thus, the tungsten component in a certain form and othervaluable can be separated and recovered at once from the raw materialmixture containing tungsten and the other valuable.

Tungsten is produced by calcining the electrolytic solution in which thetungsten component has been dissolved. Further, it is preferred in termsof production efficiency that after the step of dissolving tungsten inthe electrolytic solution, the electrolytic solution is subjected topreliminary heating, for example at 150 to 200° C., to decrease thewater content, and then calcined to produce tungsten. The calcinationmay be preferably carried out in a reducing atmosphere such as hydrogen,argon, nitrogen or the like, and more preferably in the hydrogenatmosphere.

In the calcining step, the calcining temperature is controlled to beless than 800° C. By controlling the calcining temperature in this way,the remaining of carbon in the alcohol amine compound is suppressed andthe reaction of carbon with tungsten is suppressed, thereby producingtungsten with good yield. The calcining temperature may be preferably500° C. or more and less than 800° C. If the calcining temperature isless than 500° C., the reduction reaction may be very slow.

In the method for producing tungsten according to the present invention,tungsten carbide may be produced together with tungsten aftercalcination. The ratio of the yields of tungsten carbide to tungstenproduced can be adjusted by controlling the calcining temperature.According to the present invention, an increased amount of tungsten isgenerated by controlling the calcining temperature to a lower calciningtemperature and an increased amount of tungsten carbide is generated bycontrolling the calcining temperature to a higher calcining temperature,in a rage of less than 800° C. for the calcining temperature.

According to the method for producing tungsten of the present invention,tungsten and optionally tungsten carbide may be directly produced bycalcining the electrolytic solution itself in which the tungstencomponent has been dissolved. Therefore, the method according to thepresent invention has very good production efficiency as compared withthe conventional method (as described in Patent Document 3) in which thetungsten component is dissolved in the electrolytic solution as ahydroxide by electrolysis of the raw material mixture, the hydroxide isconcentrated to form a tungstate salt compound and the salt compound isoptionally heated and reduced.

On the other hand, the valuable electrodeposited onto the cathode usedfor electrolysis may be one or more selected from the group consistingof cobalt, nickel, iron, chromium and vanadium, for example. Thesevaluables can be separated from tungsten that can be easily dissolved inthe electrolytic solution, and other residue, by a known method such ascontrolling of the pH in the acid-leaching to an alkaline side. Further,when the cathode used for electrolysis is made of, for example,titanium, stainless steel, iridium, niobium or zirconium, the abovecobalt, nickel, iron or like can be satisfactorily electrodeposited,which is preferred.

The at least one valuable that is the residue in the electrolyticsolution may be, for example, one or more selected from the groupconsisting of titanium, tantalum and silica. These valuables areelectrolytically inactive, so that they can be easily separated as theresidue without special treatment.

In another aspect, the present invention provides a method for producinga tungstate solution, comprising subjecting a raw material mixturecomprising at least one valuable containing tungsten to electrolysisusing an electrolytic solution containing an alcohol amine having 1 ormore and less than 6 carbon atoms to dissolve tungsten in theelectrolytic solution. By subjecting the raw material mixture containingthe at least one valuable containing tungsten to electrolysis using theelectrolytic solution containing the alcohol amine having 1 or more andless than 6 carbon atoms, the tungstate solution that can producetungsten with good efficiency and yield can be obtained.

EXAMPLE

Hereinafter, Examples of the present invention will be described, butthe Examples are merely for the purpose of illustration and are notintended to limit the present invention.

Example 1

10 kg of super hard material scrap having the contents as shown in Table1 was placed in a titanium basket to prepare an anode for anelectrolytic bath.

A titanium plate was used as a cathode for the electrolytic bath. 10% bymass of monoethanolamine was used as an electrolytic solution which wasprepared by adding pure water to the monoethanolamine to bring about 20L. Electrodissolution was carried out at a current density of 5 A/dm²and a constant current of 100 A at a temperature of 70° C. for 10 hours.

As a result, metallic cobalt was deposited on the surface of thetitanium plate of the cathode. Further, tungsten was dissolved in theelectrolytic solution, and a residue was generated in the electrolyticsolution. In addition, the amount of tungsten dissolved was 0.6 kg, andthe current efficiency was substantially 100%.

The electrolytic solution containing dissolved tungsten was thenpreheated at 200° C. to reduce water content, and then calcined in ahydrogen atmosphere at 780° C. XRD demonstrated that 90% of tungsten wasproduced and 10% of tungsten carbide was produced.

TABLE 1 W Co Ni Ta Fe mass % mass % mass % mass % mass % 80 12 1 2 1

Example 2

5 kg of super hard material scrap having the contents as shown in Table1 was placed in a titanium basket to prepare an anode for anelectrolytic bath.

A titanium plate was used as a cathode for the electrolytic bath.

% by mass of monoethanolamine was used as an electrolytic solution whichwas prepared by adding pure water to the monoethanolamine to bring about10 L. Electrodissolution was carried out at a current density of 10A/dm² and a constant current of 100 A at a temperature of 70° C. for 10hours.

As a result, metallic cobalt was deposited on the surface of thetitanium plate of the cathode. Further, tungsten was dissolved in theelectrolytic solution, and a residue was generated in the electrolyticsolution. In addition, the amount of tungsten dissolved was 1.1 kg, andthe current efficiency was substantially 100%.

The electrolytic solution containing dissolved tungsten was thenpreheated at 200° C. to reduce water content, and then calcined in ahydrogen atmosphere at 700° C. XRD demonstrated that 90% of tungsten wasproduced and 10% of tungsten carbide was produced.

TABLE 2 W Co Ni Ta Fe mass % mass % mass % mass % mass % 70 10 1 10 1

Comparative Example 1

The same material was used and treated in the same method as in Example1, with the exception that the calcining temperature in the hydrogenatmosphere was 1000° C. XRD demonstrated that 90% of tungsten carbidewas produced and 10% of tungsten was produced.

What is claimed is:
 1. A method for producing tungsten, comprising thesteps of: subjecting a raw material mixture comprising at least onevaluable containing tungsten to electrolysis using an organicelectrolytic solution to dissolve tungsten in the electrolytic solution;and calcining the electrolytic solution containing dissolved tungsten ata temperature of less than 800° C. to obtain tungsten.
 2. The method forproducing tungsten according to claim 1, wherein the organicelectrolytic solution is an organic alkaline electrolytic solution. 3.The method for producing tungsten according to claim 2, wherein theorganic alkaline electrolytic solution contains at least one alcoholamine.
 4. The method for producing tungsten according to claim 3,wherein the at least one alcohol amine is monoethanolamine and/ortriethanolamine.
 5. The method for producing tungsten according to claim1, wherein the raw material mixture contains from 1 to 30% by mass of atleast one valuable other than tungsten.
 6. The method for producingtungsten according to claim 5, wherein the raw material mixture containsfrom 1 to 10% by mass of at least one valuable other than tungsten. 7.The method for producing tungsten according to claim 6, wherein the rawmaterial mixture contains from 3 to 10% by mass of at least one valuableother than tungsten.
 8. The method for producing tungsten according toclaim 1, wherein the electrolysis is carried out by adjusting atemperature of the electrolytic solution to 20 to 80° C.
 9. The methodfor producing tungsten according to claim 2, wherein the electrolyticsolution has a pH of 7 or more.
 10. The method for producing tungstenaccording to claim 1, wherein tungsten carbide is obtainedsimultaneously with the tungsten in the step of calcining theelectrolytic solution containing dissolved tungsten at the temperatureof less than 800° C. to obtain tungsten.
 11. The method for producingtungsten according to claim 1, wherein after the step of dissolvingtungsten in the electrolytic solution, the electrolytic solution issubjected to preliminary heating to reduce water content, and thencarrying out the calcining step to obtain tungsten.
 12. The method forproducing tungsten according to claim 1, wherein an anode used for theelectrolysis is a titanium basket provided with the raw material mixturecontaining the at least one valuable containing tungsten.
 13. The methodfor producing tungsten according to claim 2, wherein the raw materialmixture contains from 1 to 30% by mass of at least one valuable otherthan tungsten.
 14. The method for producing tungsten according to claim3, wherein the raw material mixture contains from 1 to 30% by mass of atleast one valuable other than tungsten.
 15. The method for producingtungsten according to claim 4, wherein the raw material mixture containsfrom 1 to 30% by mass of at least one valuable other than tungsten. 16.The method for producing tungsten according to claim 2, wherein theelectrolysis is carried out by adjusting a temperature of theelectrolytic solution to 20 to 80° C.
 17. The method for producingtungsten according to claim 3, wherein the electrolysis is carried outby adjusting a temperature of the electrolytic solution to 20 to 80° C.18. The method for producing tungsten according to claim 4, wherein theelectrolysis is carried out by adjusting a temperature of theelectrolytic solution to 20 to 80° C.
 19. The method for producingtungsten according to claim 5, wherein the electrolysis is carried outby adjusting a temperature of the electrolytic solution to 20 to 80° C.20. The method for producing tungsten according to claim 6, wherein theelectrolysis is carried out by adjusting a temperature of theelectrolytic solution to 20 to 80° C.